Jenkins Kata 5: Docker Container Build Step

Step 1: Add a Dockerfile#

To do this:

• Use the NGINX image and copy the files to the container.

• Enter the following into the text editor:

• Save the changes.

Build the Dockerfile as follows:

Cody’s first step in containerizing the “web-storelist” application is to add a Dockerfile. The Dockerfile contains directives that copy the files of the application to an image based on the official NGINX image. NGINX is an open-source HTTP server. Cody then tests the Dockerfile by building it manually with the docker build command.

Run the image locally as follows:

The commands to add the Dockerfile to Cody’s repository index, commit, and push are given below:

These commands commit the addition of the Dockerfile to the local “web-storelist” Git repository, then push that commit to the Gogs server. If we return to Jenkins, we should see a new, recent build in the “web-storelist” job. When the commit was pushed to Gogs, the webhook executed and triggered the build. We can also view the workspace of the job and should see the Dockerfile in the list of files. The job pulled the “web-storelist” repository when it was executed, updating the workspace with the latest commits.

Step 2: Install the Docker plugin#

The following commands to install the Docker plugin:

• Click Jenkins at the top left.
• Click “Manage Jenkins.”
• Click “Manage Plugins.”

• Click the “Available plugins” tab.
• Enter “docker build” in the filter field.
• Check the box next to “Cloudbees Docker Build and Publish” plugin.
• Click “Install without restart.”
• Wait for install to complete.
• Click “Go back to the top page.”

This step installs another Jenkins plugin, the Cloudbees Docker Build and Publish plugin. Jenkins is an open-source system. Cloudbees is a company that offers Jenkins with enterprise services. This plugin is provided as free open source by Cloudbees.

The Cloudbees Docker plugin supports building and uploading images. These things could be done with a shell script, but the plugin simplifies the job configuration. The complexities of image build and publication are handled by it. As we’ll see in a later step, only four configuration values are required to build and publish a new image.

Step 3: Run a private Docker registry#

Return to the terminal window and run the following command:

Docker images can be uploaded to a public repository, such as Docker Hub. Public repositories are typically used to share public, open-source images. The “web-storelist” application isn’t exactly private, but it also isn’t very useful to anyone but the Coder family. Cody has, therefore, decided to publish the “web-storelist” image to a private repository instead of the public Docker Hub.

Docker Hub provides a private repository image called registry. Cody runs the registry container locally, so the Jenkins job can upload images to it as they’re built. When the images are deployed as running containers, they will be pulled from the private repository.

Step 4: Add a Docker build#

The following are the steps to add a Docker build:

• Click the “Jenkins” icon at the top left.
• Select the “web-storelist” job.
• Click “Configure.”

• Select the “Build Steps” tab.
• Click “Add build step.”
• Select “Docker Build and Publish.”

• Repository Name: “dk/storelist.”
• Tag: “${BUILD_NUMBER}”
• Docker host URI: “unix:///var/run/docker.sock”
• Docker registry URL: “https://ed-6091404232622080.educative.run:3000/”
• Click the “Advanced” option and then select the “Skip Push” option.
• Click “Save.”

Installing the Cloudbees Docker plugin added a new option to the “Add build step” selection list: Docker Build and Publish. This plugin-provided step requires four parameters to build and publish new images to a repository.

The CI pipeline we’re building has taken another step forward: It now includes a build process. Executing the “web-storelist” Jenkins job pulls the latest code from the repository. The build process then creates a new “dk/storelist” Docker image each time the job executes and uploads it to the private repository, where it’s ready to be deployed as a container.

To run the “web-storelist” job, do the following:

• Click “Build Now.”

This step executes the “web-storelist” job with the Docker Build and Publish step. Note that the build history entry format has changed. It’s no longer just a number. The new build history entry format includes all the tags that were assigned to the new image that was built.

A single Docker image can be assigned multiple tags. The default configuration of the Docker Build plugin assigns two tags to each image on every build. The first is the tag that’s defined in the configuration (this is set to the ＄{DOCKER_BUILD} environment variable.) The second is latest.

If a tag is not specified when the docker container run command is executed, Docker will look for an image with a latest tag and run that one. The Docker Build plugin assigns a latest tag to each new image, which moves the tag from the previous image built to the newest one. This ensures that each run of the “dk/storelist” image will run the most recently built one by default. It’s still possible, if needed, to run a previously built container by specifying a prior tag in a docker container run command.

Run the following command:

The command above will display all the running images. We have to copy the image name of “/dk/storelist” and run the container of that image using the following command: